1. Technical Field
The present invention relates to a switching device that has a switching element made of a semiconductor element.
2. Background Art
Conventionally, there has been provided a switching device that has a switching element being a contactless switching element such as a triac, a thyristor, and a field-effect transistor (FET), and is configured to turn off and on (non-conduction and conduction) the switching element. This switching device performs a switching of power to be supplied from a power supply to a load, by having the switching element inserted between the load and the power supply of an illumination device or the like, for example.
In recent years, as a switching element that is used in this type of a switching device, attention is being focused on a semiconductor element that uses a nitride semiconductor such as gallium nitride (GaN) and a wide band-gap semiconductor such as silicon carbide (SiC). As an example of this type of a semiconductor element, there is an element that uses a 2-dimensional electron gas layer generated in an AlGaN/GaN hetero-interface as a channel layer (for example, see Unexamined Japanese Patent Publication No. 2010-176885; hereinafter, Patent Document 1).
According to the switching element described in Patent Document 1, a GaN layer and an AlGaN layer are stacked, and a first electrode, a second electrode, and an intermediate-potential part are formed on the surface of the AlGaN layer. Further, a gate (control electrode) is formed on the intermediate-potential part. Based on this configuration, in the switching element, a current flowing in the path between the first electrode and the second electrode changes, by a gate voltage (control signal) applied to the gate, in a state of a voltage being applied between the first electrode and the second electrode. In short, this switching element constitutes a normally-off type switching element in which the current path between the first electrode and the second electrode becomes non-conductive when the gate voltage becomes lower than a predetermined threshold value, and the current path between the first electrode and the second electrode becomes conductive when the gate voltage exceeds the threshold value.
A switching device that uses the switching element of the above configuration can minimize an ON resistance as an electric resistance that is present in the current path in the conductive state, as compared with the case of using a MOSFET (Metal-Oxide-Semiconductor FET), an IGBT (Insulated-Gate-Bipolar-Transistor), and the like.